A typical two-pole circuit breaker (for example, a residential two-pole circuit breaker) receives as inputs two line voltages and a neutral voltage. The two line voltages (line-to-neutral voltages) typically are 120V alternating current (“AC”) signals, 180 degrees out of phase from one another. Each line voltage alternates in polarity with respect to the neutral voltage, which is determined from the two line voltages in a conventional manner. The sum of the two line voltages (the line-to-line voltage) is a 240V AC voltage.
A microprocessor or controller in the circuit breaker can be used to measure line voltages. For example, circuits can be used to divide a line voltage and output the divided signal to the microprocessor. The microprocessor includes an analog to digital (A/D) converter to receive the analog voltage and convert it to a digital voltage for measurement by the microprocessor.
Basic AC voltage power quality is expected throughout a system employing a circuit breaker. Due to variations in the distribution network upstream from the circuit breaker, the AC voltage is expected to vary within a certain range. Variations in the AC voltage outside of this range could damage the circuit breaker or components (such as appliances) downstream from the circuit breaker. For example, metal oxide varistors (MOVs) in many components will heat up when subjected to a prolonged overvoltage and eventually fail. Other downstream components can similarly fail if subjected to prolonged overvoltage conditions. Likewise, circuit breakers often include MOVs or other components that can fail if subjected to a prolonged overvoltage condition.
Currently, circuit breakers are tripped based on measurements of current rather than voltage. A gradual increase in voltage will not cause these circuit breakers to trip. What is needed is a way to detect such improper voltage conditions by monitoring a line-to-neutral voltage and/or a line-to-line voltage and take appropriate action to limit the effect of improper voltages on the circuit breaker and downstream components.